Microbial decontamination of soils contaminated with hydrocarbons, in particular mineral oils by microbial oxidation

Abstract

The microbial decontamination of soils contaminated with hydrocarbons, in particular with mineral oils, by microbial oxidation is improved by a process in which in addition to supplying the oxygen necessary for degradation, by aeration, soluble nutrients, water and soluble or dispersed biosurfactants as such or mixed with chemical surfactants are metered into the contaminated soils directly or into the removed contaminated soil layers, in one or more batches at time intervals, in an amount such that the formation of toxic intermediates which slow down or block microbial degradation in prevented, the accessibility of mineral oils and their products for the microorganisms is simultaneously increased and, as a result, accelerated, virtually complete mineralization by respiration to CO 2 and H 2 O is effected.

We claim: 
     
       1. In a process for the decontamination of soils contaminated with hydrocarbon which process consists essentially of aerating the soil with oxygen necessary for degradation of the hydrocarbon, adding water and surfactants, whereby the hydrocarbon is converted to carbon dioxide and water, the improvement wherein the surfactant comprises a biosurfactant. 
     
     
       2. The process of claim 1 wherein the surfactant comprises a mixture of (a) a biosurfactant and (b) a synthetically produced chemical surfactant in a weight ratio of from 0.1:1 to 1:1. 
     
     
       3. The process of claim 1 wherein the biosurfactant comprises a hydrophilic moiety containing at least one saccharide and a hydrophobic moiety containing at least one functionalized fatty acid. 
     
     
       4. The process of claim 3 wherein the biosurfactant is a member selected from the group consisting of trehalose dicorynomycolate, trehalose lipid triesters, and rhamnose lipids. 
     
     
       5. The process of claim 1, wherein the biosurfactant is (a) at least one glycolipid having the structural formula: ##STR9## wherein, in formulae I and II, the glycosidic bond 1,1; 1,2; 1,3; 1,4; 1,6 in the anomeric forms α,α; a,β; β, β and the groups R 1  to R 3  in the positions 1, 2, 3 and 4 are in the cis or trans configuration, and R 1  to R 3  are each hydroxyl, alkoxy, alkylcarbonyloxy, alkylcarboxamido or amino and R 4  is hydroxymethylene, aminomethylene, alkoxymethylene, alkylcarboxamido-N-methylene, carboxyl, carboxamido, alkoxycarbonyl or N-alkylcarboxamido, and in R 1  to R 4  the alkyl groups are the same or different and contain 8 to 60 carbon atoms or (b) a trehalose lipid tetraester of the formula ##STR10## where R 1  is ##STR11## or --OC(CH 2 ) y  COOH and R 2  is ##STR12## CH 3 , where x is from 4 to 22, y is from 1 to 4 and z is from 4 to 22, and R 3  is H or alkyl. 
     
     
       6. The process of claim 1, wherein the biosurfactant is selected from the group consisting of (a) an anionic rhamnose lipid, 2-O-α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoic acid of the structural formula: ##STR13## (b) an α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoic acid of the structural formula: ##STR14## (c) a rhamnolipid having a β-hydroxydecanoyl radical in the molecule (with a molecular weight of 334 or 480) of the structural formula: ##STR15## and (d) an β-L-rhamnopyranosyl-β-hydroxydecanoic acid (rhamnolipid or 2-O-α-L-rhamnopyranosyl-β-L-rhamnopyranosyl-β-hydroxydecanoic acid) of the structural formula: ##STR16## 
     
     
       7. The process of claim 1 wherein the contaminated soil is additionally treated with at least one bacterial nutrient which is a water-soluble salt of a compound selected from the group consisting of Na, K, Ca, Mg and Fe. 
     
     
       8. The process of claim 7 wherein the salt is (NH 4 ) SO 4 , MgSO 4 .7H 2  O, KCl, CaCl 2 .2H 2  O, CaCl 2 .6H 2  O or FeCl 3 .6H 2  O. 
     
     
       9. The process of claim 1 wherein contaminated soil layers are removed, introduced into at least one reactor and fluidized therein with water, with the addition of nutrients, at a constant temperature in the range from 10° to 40° C. and at pH of from 4 to 8 and with the addition of a surfactant which comprises an anionic or nonionic biosurfactant, with aeration of the contaminated soil layers with the natural microorganism population present therein, for rapid microbial oxidation of the hydrocarbons with formation of CO 2  and an aqueous solution to form a mixture of a solid phase and a liquid phase which contains hydrocarbon-free solid and a biomass, separating the mixture containing the solid phase and the liquid phase from the aqueous solution and removing the aqueous solution. 
     
     
       10. The process of claim 9 wherein the surfactant comprises a mixture of a nonionic or anionic biosurfactant and a synthetically produced chemical surfactant. 
     
     
       11. The process of claim 9, wherein the aeration rate is from 0.05 to 1.0 liters (S.T.P.) of air per liter of reactor volume per minute. 
     
     
       12. The process of claim 9 wherein the conversion is carried out in a continuous procedure. 
     
     
       13. The process of claim 9 wherein a plurality of reactors is used and at least one reactor is a mechanically stirred reactor and at least one reactor is a hydrodynamic reactor. 
     
     
       14. The process of claim 1, wherein comminuted bark is additionally added. 
     
     
       15. The process of claim 14 wherein the bark is pine bark. 
     
     
       16. The process of claim 1 wherein from 0.5 to 20 g of biosurfactant is added per kg of hydrocarbon. 
     
     
       17. The process of claim 1, wherein the decontamination of the soil is carried out in situ by a procedure in which compressed air in combination with surfactant composition containing at least one of a nonionic biosurfactant is sprayed as a dispersion into the contamination soil through a flexible pipeline system, which pipeline has orifices arranged at intervals, whereby the natural microorganism population present in the soil is enhanced and microbial oxidation of the hydrocarbon to CO 2  and H 2  O is accelerated. 
     
     
       18. The process of claim 17 wherein the surfactant composition further contains a synthetically produced chemical surfactant.